Sealed coaxial connector



A. DARNOIS SEALED COAXIAL CONNECTOR Feb. 7, 1967 2 Sheets-Sheet 1 Filed July 2, 1964 United States Patent O M 11 Claims. (Cl. 174-88) The present invention relates to coaxial connectors and more particularly to hermetically sealed coaxial connectors.

The use of coaxial connectors in high frequency and very high frequency current techniques is well known. Such devices are used as connection elements, for example, between an electronic tube and a wave guide, or again between a wave guide and an antenna. These connectors are generally constructed with two coaxial conductors, one of which is centered with respect to the other by means of a part which serves simultaneously as a guide insulator, and a centering element by sliding on to the two conductors. Cases may occur in which one of the elements to be connected is under vacuum and in this case the coaxial connector must be hermetically sealed. In some cases, for reasons of propagation, it is also desirable that the two conductors be of the same material and that the material be selected from among the most highly conductive available, such as copper.

It is an object of the present invention to provide a hermetically sealed coaxial connector capable of handling high frequency currents.

Another object of the present invention is to provide a coaxial connector which can be readily mounted on and dismantled from the elements which it is to connect.

Briefly, according to the invention, the hermetically sealed coaxial connector comprises an internal and external condu-ctor, both made of the same metal, such as highly conductive copper. The internal conductor is centered with respect to the external conductor by means of a refractory member through which it passes, such as a ceramic rich in aluminium oxide. The refractory member has an external diameter Very near to the internal diameter of the outside conductor and is composed of at least two constituent parts. The internal conductor is at least partly hollow, that is, it has an axial thin-walled cavity extending at least to the region of the hermetic seal. A metal part with a coeicient of expansion similar to that of the material forming the hermetic seal and of suicient length to project on either side of the region of the hermetic seal, is located within said cavity. The hermetic seal is formed by a glass placed over the refractory member, for example a borosilicate glass. The glass is melted in a controlled atmosphere and bonds to the internal wall of the outside conductor and the external wall of the internal conductor, as well as to one of the surfaces of the refractory member while the inner metal part prevents separation of the internal conductor from the glass. This surface preferably has previously been covered with a layer of a material facilitating the bonding of the glass.

According to a feature of the invention the metal part located in the cavity of the central conductor is provided with a longituidnal channel to permit escape of air, or gas trapped therebelow in the cavity and is made of a 3,303,268 Patented Feb. 7, 1967 ICC material having a coeilicient of expansion similar to that of the glass forming the hermetic seal.

According to another aspect of the invention, the inner and outer conductors, the refractory member, and the centr-al metal core are assembled, and then the glass used to effect the hermetic seal is deposited in powder form at the location, and in such distribution, which it is to occupy after the connector is finished. The assembly is then heated in a controlled atmosphere until the glass fuses and bonds to the conductors, and the refractory member, so that a unitary, sealed connector is obtained.

In order that the invention may be more fully understood, some embodiments thereof will now be described, by way of example with respect to the accompanying drawings, in which:

FIGURE 1 is a sectional elevational view of an embodiment of coaxial connector according to this invention; and 1 FIGURE 2 is a similar sectional view of another embodiment of the connector, for use with three conductors.

Referring to FIGURE l, the coaxial connector comprises an outer conductor 1 and an inner conductor 2, both of the same metal which is capable of withstanding the high temperature at which sealing is effected and preferably highly conductive. For example, the conductors may be made of highly conductive copper which does not contain gas, in particular oxygen known commercially as OFHC (oxygen free high conductivity) copper. The external conductor comprises connecting flanges 3 and 4 for attaching the connector to the elements to be connected. The flange 4 which is on the side connectable to an apparatus under vacuum is provided with a groove 5 intended to receive a plastic sealing joint (not shown). In the region of the hermetic seal between the two conductors and therebeyond the thickness of the outer conductor is reduced as shown at 6, to a few tenths of a millimeter. The outer conductor also comprises an internal shoulder 7.

The inner conductor 2 comprises a solid portion 8, and an axial cavity 9 of a length such that it is located on either side of the seal. The walls 10 of this cavity are similarly several tenths of a millimeter thick. In the cavity 9 is located, with snug, but not forced fit, a metal part 11 provided with a longitudinal channel 12. Part 11 is made of a metal such as molybdenum, having a coeicient of expansion similar to that of the glass serving to effect the hermetic seal; the channel 12 aids in making the assembly, provides for uniform circumferential ex pansion upon heating, and permits evacuation of the assembly by providing access to the pocket formed below the part 11 and removal of any -air or gases trapped therebelow.

The internal conductor 2 terminates in connecting portions 13 and 14, and it is centered in the external conductor by means of 'a refractory member 15, of sintered aluminium oxide for example, which rests upon the shoulder 7 and which is provided with a central aperture of a diameter adjusted to the external diameter of the inner conductor 2. Connecting portion 14 is shown as a separate insert secured, for example by soldering, to inner conductor 2.

yIn order to resist stress as after cooling, the member 15 is first provided with a cut along a diameter and throughout its thickness so that in effect it is formed of two matching parts. It .may also be provided on its 3 surface 16 with a layer of material serving to facilitate the heat bonding of the sealing glass, such as a layer of enamel.

The glass serving to effect the hermetic seal 17, such as a borosilicate, is introduced in powder for-m into the annular space between the two conductors once the connector has been mechanically assembled. This powder is given a concave form (as viewed in cross section) by means of a suitable tool. The assembled connector thus prepared is placed in a furnace having a controlled atmosphere, such as a reducing, or inert gas, for example hydrogen, or argon, and brought to a temperature of approximately 1050" C. for the period necessary for the melting of the powdered glass which, when molten, slowly rises by capillary attraction along the surfaces of the two conductors; the assembly is then slowly cooled. =In the coaxial connect-or thus produced the glass 17 is subjected to compressive stresses which `gives rigidity to the seal. The thin wall of region 6 of the outer conductor, as well as the thinwalls 10 of the inner conductor, in the region of the seal, provide for a tight seal since the thin copper walls follow the glass as it cools. Central metal part 1.1 prevents separation of the copper of the inner conductor walls 10 from the glass upon cooling. The copper walls 10 are retained tight against the glass since the coefficient of expansion of the central metal part 11 is matched to that of the glass.

A variation of the invention, as shown in FIGURE 2, consistsin forming a connector having two inner coaxial sealed conductors arranged in a concentric manner. A triple conductor assembly of this type is formed according to this embodiment by an external conductor 18, a first internal conductor 19 and a second inner conductor 20, arranged within the conductor 19. All the conductors are of the same metal which is preferably highly electrically conductive very pure copper, able to withstand the high temperature'of formation of the seal. The external conductor 18 comprisesV a flange 21 for attachment to the'elernents to be connected. As in the Vembodiment of FIGURE 1, the external conductor cornprises in the region of the hermetic seal and therebeyond a thinner portion 22 and a shoulder 23. The first internal conductor 19 is a `thin tube and the second internal conductor 20 is partly tubular and partly solid. The transition between the tubular and solid portions is effected at 24 in the region of the lower part of the hermetic seal. AIn the tubular portion 25 of the second internal conductor is located with a snug t a metal part 26, of molybdenumv for example, having a coefficient of expansion similar to that of the glass serving to form the seal. This part 26 is provided with a longitudinal channel 2,7.

Between the external conductor 13 and the internal conductor 19 and resting upon the shoulder 23 is located a refractory member 2S, of sintered aluminium oxide for example, which is provided with a central aperture of a diameter matching the external diameter of the conductor 19. The member 28 is previously provided with a slit along a diameter and throughout its thickness so that in effect it is formed of two matching parts. It may be covered on its surface 29 with a layer of a material, such as enamel, serving to facilitate the heat bonding of the glass forming the seal.

'In the same manner there rests upon the shoulder 29 ofthe inner conductor 19, a two-part member 3d of sintered aluminium oxide `for example, which is slitY throughout its thickness along a diameter and which may also be provided with a layer of enamel on its surface 31 and has an aperture just sufficient to accommodate the conductor 20.

Once the conductors 1,8, 19 and 20 have been assembled with the refractory parts 28 and 30, the `glass 32 serving to effect the double seal, such as a borosilicate, is introduced in powder .form into the spaces reserved therefor. A tool is used to give to this powder a concave form. The assembly is introduced into a furnace having a controlled atmosphere and brought to a temperature of the order of 10S-0 C. for the time necessary for the powdered glass to melt. The molten glass rises by capillary effect, as shown at 33, 34 and 35 along the three conductors 18, 19 and 20. After cooling the glass is subjected, as in the example of FIGURE 1, to compressive stresses, which impart rigidity to the hermetic seal.

Whilst particular embodiments have been described, it will be understood that various modications may be made without departing from the scope of this invention as defined by the following claims. i

I claim: t

1. A hermetically sealedv coaxial connector comprising an external tubular conductor and at least one coaxially arranged inner conductor, the inner conductor being hollow at least in the region of the hermetic seal, each of said conductors being formed with a thin walled tubular portion at least in the region of the hermetic seal; a metal member arranged and snugly fitting within the tubular portion of the innermost conductor in the region of the hermetic seal; a refractory member formed of at least two parts located between adjacent conductors in the region of the hermetic seal to hold said conductors in spaced relationship; and heat-formed hermetic seal substance located over an exposed surface of said refractory member and fused and bonded to the conductors; said metal member being of a material having a coefficient of expansion similar to that of the heatformed hermetic seal substance.

2. A coaxial connector as claimed in claim 1 in which said metal member is formed with a longitudinal channel to provide for removal of gases therebeneath.

3'. A coaxial connector as claimed in claim 1 in which the thickness of the wall of the external tubular conductor is reduced in the region of the hermetic seal.

4. A coaxial connector as claimed in claim 1, said exposed surface of the refractory member being coated with said heat-formed hermetic seal substance, whereby said subs-tance will become bonded to said refractory member, and to said conductors.

f5. A coaxial connector as claimed in claim 1 said heat-formed hermetic seal substance bein-g fused, powdered glass.

6. A coaxial connector as claimed in claim 5, said glass being a borosilicate glass.

7. A coaxial connector as claimed in claim 1, said refractory member being formed of sintered aluminium oxide.

8. A coaxial connector as claimed in claim `1, the wall thickness of each. conductor in the region of the hermetic seal being a fewtenths of a millimeter.

V9. A hermetically sealed coaxial connector comprising an external tubular conductor and an internal conductor, both of said conductors being made of a highly conductivemetal, at least one of said conductors being formed with a projecting shoulder, said internal conductor being located along the axis of said external conductor, a refractory spacer member formed with a passage through which said internal conductor passes, said refractory member resting on said shoulder within the external conductor, said internal conductor comprising both a solid portion and a tubular portion, said tubular portion defining a cavity extending at least to the region of the hermetic seal between the two conductors, and a heat-formed hermetic seal supported on said refractory member and bonded to both the external conductor and the internal conductor, and a metal member of a material having a coeicient of expansion similar to that of the heat-formed hermetic seal located with a snug t within said cavity.

16. A coaxial connector as claimed in claim 9, in

which the refractory member is formed of at least two constituent parts,

11. A coaxial connector as claimed in claim 9, wherein said seal is further bonded to said refractory member.

References Cited by the Examiner UNITED STATES PATENTS 2,093,567 9/1937 McCullough 174-50 X 6 Cuttler. Scharfnagel 174-5061 X Smith 174-5061 X Edelman 174-818 X LEWIS H. MYERS, Primary Examiner.

D. L. CLAY, Assistant Examiner'. 

1. A HERMETICALLY SEALED COAXIAL CONNECTOR COMPRISING AN EXTERNAL TUBULAR CONDUCTOR AND AT LEAST ONE COAXIALLY ARRANGED INNER CONDUCTOR, THE INNER CONDUCTOR BEING HOLLOW AT LEAST IN THE REGION OF THE HERMETIC SEAL, EACH OF SAID CONDUCTORS BEING FORMED WITH A THIN WALLED TUBULAR PORTION AT LEAST IN THE REGION OF THE HERMETIC SEAL; A METAL MEMBER ARRANGED AND SNUGLY FITTING WITHIN THE TUBULAR PORTION OF THE INNERMOST CONDUCTOR IN THE REGION OF THE HERMETIC SEAL; A REFRACTORY MEMBER FORMED OF AT LEAST TWO PARTS LOCATED BETWEEN ADJACENT CONDUCTORS IN THE REGION OF THE HERMETIC SEAL TO HOLD SAID CONDUCTORS IN SPACED RELATIONSHIP; AND HEAT-FORMED HERMETIC SEAL SUBSTANCE LOCATED OVER AN EXPOSED SURFACE OF SAID REFRACTORY MEMBER AND FUSED AND BONDED TO THE CONDUCTORS; SAID METAL MEMBER BEING OF A MATERIAL HAVING A COEFFICIENT OF EXPANSION SIMILAR TO THAT OF THE HEATFORMED HERMETIC SEAL SUBSTANCE. 